JP5708331B2 - Steel welded joint structure - Google Patents

Description

  The present invention relates to a welded joint structure of steel suitable for welding ultra-high strength steel.

Recently, with the progress of high-rise and large-scale building structures, application of 800 N / mm ² class ~1000N / mm ² grade ultra-high strength material has emerged as a steel pillar material. Although application of ultra-high strength material is suitable for slimming the column cross section, there is a technical problem in securing the performance of the welded joint.
A weld joint applied to a building structure is generally a so-called overmatching joint in which the material strength of the welded portion is higher than the material strength of the base material.

However, a welding material for realizing an overmatching joint that exceeds the strength of the base material, which is an ultra-high strength material of 800 N / mm class ^{2 to} 1000 N / mm class ² , is weld cracking compared to a welding material of lower strength. (Initial cracks) are likely to occur, and in order to prevent this, strict prognostic heat management and welding heat input and temperature limits between passes are required. Application of an object to a joint is subject to very strict construction conditions, and the productivity of the welded joint is significantly reduced.

  On the other hand, soft joints with so-called undermatching, in which the material strength of the weld is lower than that of the base metal, are less susceptible to weld cracking compared to the application of high-strength welding materials, and are low cost and prognostic heat management There is a merit that the conditions of welding heat input and interpass temperature are relaxed, and there are examples of application to penstock and the like. As for the soft joint, it is conventionally known that a weld joint exceeding the tensile strength of the base material can be obtained depending on the shape condition of the welded portion.

  For example, the strength of a soft joint depends on the relative thickness of the soft weld (the ratio of the thickness of the soft weld to the plate thickness). The smaller the relative thickness, the higher the joint strength and the tensile strength of the base metal. It is also possible to exceed (for example, refer nonpatent literature 1).

  However, in order to reduce the relative thickness of the soft weld, it is necessary to use a so-called narrow groove welding in which the groove dimension of the weld is reduced. It is difficult to ensure strict narrow gaps due to errors in dimensions and construction, and even if narrow gaps can be secured, special welding skills and Requires technology.

  In addition, the application of so-called partial soft joints, in which a welding material with a strength lower than the base metal strength is applied to only a part of the weld layer on the root side, not all of the weld metal, prevents cracking of the initial layer on the root side. It is known that it is highly effective in preventing brittle fracture when subjected to a tensile force.

In addition, the root-side first layer of a welded joint with a grooving groove is welded with a welding material that has lower strength and higher ductility than the base material, and the remaining layers are welded with strength equal to or higher than that of the base material. A welding method for a partial soft joint that is welded with a material has been proposed (see, for example, Patent Document 1). Furthermore, in Patent Document 1, a root-side initial layer or a plurality of layers less than 1/3 of the base metal plate thickness of a welded joint of a 490 N / mm ² base metal groove is lower in strength and higher in ductility than the base material. It is exemplified that the fracture of the base material can be confirmed with a test body to which the above welding material is applied.

Japanese Patent No. 3820493

"Dimensional effect on static strength of welded joints including soft layer", Journal of the Japan Welding Society, Vol. 37, No. 11, 1968

Incidentally, the technique disclosed in Patent Document 1, for the base material of higher strength than 600N / mm ² class, instances where the root-side first layer or layers are applied weld material having a high ductility at lower strength than the base metal is expressly It has not been. Although the application conditions for overmatching welding are more severe, welded joints of 800 N / mm class ^{2 to} 1000 N / mm class ² ultra-high-strength steel materials have great merit of applying partial soft joints. In the prior art disclosed in Patent Document 1, it is not clear.

The present invention has been made in view of the above circumstances, and is applicable to on-site construction mainly for welded joints of ultra-high-strength steel materials of 780 N / mm ² or more, suppressing initial layer cracking and preventing brittle fracture. An object of the present invention is to provide a welded joint structure having a joint strength higher than that of the base material while applying a partially soft joint having a high effect to the above.

When the above-mentioned partial soft weld joint receives a tensile force that gradually increases in the axial direction, the soft weld on the root side is first plasticized. At this time, compressive strain corresponding to the Poisson's ratio is likely to occur in the soft weld (the lower strength part of the weld metal base material), but the higher strength base material and the other homogeneous welds (weld metal base material). Therefore, a triaxial tensile stress is generated inside the soft weld and the apparent axial strength of the weld metal is increased.
For this reason, it is possible to manufacture a joint having a strength higher than the joint strength obtained from the respective areas of the low-strength soft weld and the higher-strength homogeneous weld and the simple sum of the strengths.

The present inventors, in particular a ^{780N / mm 2 (800N / mm} 2 class) or ultra high strength steel as a base material, the weld joint using a weld metal strength is lower than the base material strength in a part of the joint Numerical analysis was performed by FEM (Finite Element Method), and the requirement of a welded joint having high joint strength was considered.
In the numerical analysis by FEM, the analysis was performed by changing each parameter shown in FIG. 1 as shown in Table 1.

  The steel joint structure in FIG. 1 includes a base material (steel material) to which reference numeral 1 is welded, a groove provided to the base material 1, a weld metal provided to the inside of the groove 2, and reference numeral 3. Reference numeral 5 is a route of the welded portion, reference numeral 6 is a soft weld portion formed on the route 5 side of the weld metal 3 and having a lower strength than the base material 1, and reference symbol 7 is formed on the soft weld portion 6 and is a base material. 1 is a homogenous weld having a strength equal to or greater than 1. Reference numeral 9 is a backing metal. In this numerical analysis, the influence of the backing metal 9 on the strength of the welded joint is ignored because the backing metal does not exist, and the homogeneous weld 6 has the same strength characteristics as the base material 1. It was.

Further, the thickness of the base material 1 is to, the thickness of the soft weld 6 is tw, the root gap is g, the groove width of the groove 2 is W, and the groove angle of the groove 2 is θ. To do.
The analysis results were summarized by the dimensionless strength σw / σo of the joint obtained by making the joint strength σw dimensionless with the base material strength σo, and the joint parameter α expressed by the equation (2).

Here, if σw / σo ≧ 1 is satisfied, it means that the joint strength is higher than the base metal strength.
Further, since the soft welded portion thickness tw is thinner and the groove width W is smaller, the joint strength tends to increase, and when the groove angle θ is larger, the joint strength tends to decrease. (2) As shown in the equation, the dimension was made non-dimensional with the base material plate thickness to, and the product of these was used as a parameter.

Regarding the numerical analysis results, the vertical axis represents the value of σw / σo (dimensionless strength of the joint), and the horizontal axis represents the value of α in equation (2). As shown in FIG. Each graph shows the result of numerical analysis for each combination of the base metal strength and the soft weld strength among the conditions shown in Table 1. The dimensionless strength σw / σo of the joint 1 shows the relationship with the value of α in equation (2) in the case of each combination of shape conditions other than the above-described strength conditions shown in FIG.
Also, FIG. 2 shows the results when the soft weld strength base metal strength is 980 N ^/ mm 2 in Table 1 (1000 N / mm ² class) is ^{590N / mm 2 (600N / mm} 2 class), Figure 3 base material strength in Table 1 indicates the results when the soft weld strength ^{780N / mm 2 (800N / mm} 2 class) is ^{590N / mm 2 (600N / mm} 2 class), the base material 4 is in Table 1 FIG. 5 shows the results when the strength is 980 N / mm ² (1000 N / mm ² grade) and the soft weld strength is 490 N / mm ² (500 N / mm ² grade), and FIG. 5 shows the base material strength in Table 1 is 780 N / mm. ² (800 N / mm class ² ) and the soft weld strength is 490 N / mm ² (500 N / mm class ² ).
In addition, each mark of the graph has a groove shape with a groove shape and a groove angle θ of 30 degrees, and a mark shape with a groove shape of 45 degrees, and a groove shape with a V shape and a groove angle θ of 30 degrees. This corresponds to the case of the V type and 45 degrees. The same five marks correspond to cases where the thickness of the soft weld layer is 3, 6, 9, 12, and 18 mm, respectively.

2 to 5, there is a correlation between σw / σo and parameter α, and σw / σo is 1 or more, that is, the shape condition that allows the partial soft joint to exhibit strength higher than the base material strength is that the base material strength is 980N. / mm ² of the base material and the soft weld strength is alpha ≦ a combination of 590N / mm ² 0.50, and so on to, ≦ alpha in matrix × 590N / mm ² of the soft weld 780N / mm ² 0. if 80,980N / mm ² of the matrix × 490 N / mm ² of the matrix × 490N / mm α ≦ 0.47 in the soft weld ² of the soft weld α ≦ 0.40,780N / mm ² Good.

However, as shown in the graphs of FIGS. 2 to 5, the parameter α in the formula (2) is established when the value of α is changed with a combination of the same base material and welding material (soft solution). This is not possible if the base material and the welding material (soft melt) are different. For example, in a combination of 1000 N / mm ² grade base material and 600N / mm ² class welding material, a combination of 800 N / mm ² grade base material and 600N / mm ² class welding material, .sigma.w / NA: 0.75, o is 1 or more α In addition, the value of the parameter α in the combination conditions of the strengths of the base material and the welding material (soft melt) other than the case analyzed this time is not clear.
Therefore, when the effects of the base metal strength and soft weld strength were taken into account and arranged, the parameters β expressed by equation (1) included the effects of the base metal strength and soft weld strength. It can be expressed in a unified manner.

The numerical analysis results are shown in FIG. 6 as a graph of the σw / σo-β relationship in which the vertical axis is the value of σw / σo (dimensionless strength of the joint) and the horizontal axis is the value of β in equation (1). In FIG. 6, as in FIGS. 2 to 5, the relationship between the values β and σw / σo corresponding to the conditions shown in Table 1 is related to the strength of the base metal and the soft weld. It is plotted in one graph. As shown in the graph of FIG. 6, the strength of the base material is 1000 N / mm class ² or 800 N / mm class ² and the strength of the soft weld is 600 N / mm class ² or 500 N / mm class ² . Also in the case of a combination of a base material and a soft weld, a correlation with β can be confirmed.
In this case, the shape condition for σw / σo to be 1 or more is β ≦ 0.15.

The present invention has been completed by obtaining the above knowledge.
That is, the steel welded joint structure of the present invention is a steel welded joint structure for connecting steel materials, and the shape of the groove is a L shape or a V shape, and the weld metal in the groove is composed of a plurality of layers. A soft welded portion comprising a plurality of layers including the first layer of the weld metal on the route side connecting the base material, the strength of the base material to be connected is 780 N / mm ² or more. The strength is 490 N / mm ² or more and is lower than the strength of the base material, and a plurality of beads are further stacked on the soft weld portion to have a strength equal to or higher than that of the base material. And the soft weld is constrained by two base metals and the homogeneous weld, and the remaining layers of the weld metal except the soft weld have a strength equal to or higher than that of the base metal. And the thickness of the base metal to the soft weld (1) from the shape represented by the thickness tw, the groove width W of the groove, and the groove angle θ of the groove, the base material strength σo, and the strength σs of the soft weld on the root side The parameter β expressed by the equation is 0.15 or less.

  In the present invention, the shape represented by the plate thickness to of the base material, the thickness tw of the soft weld, the groove width W of the groove, and the groove angle θ of the groove, By setting the parameter β expressed by the equation (1) to 0.15 or less from the material strength σo and the strength σs of the soft weld on the root side, the strength of the welded joint can be equal to or higher than that of the base metal. it can.

According to the welded joint structure of steel material of the present invention, when welding a super-high strength steel material of 780 N / mm ² or more, it is applicable to on-site construction, and is highly effective in suppressing initial layer cracking and preventing brittle fracture. The joint strength can be higher than the base material strength while applying the partial soft joint.

It is the schematic which shows the welded joint structure of the steel materials which concern on embodiment of this invention. It is a graph which shows the relationship between the dimensionless intensity | strength (sigma) w / (sigma) o of a joint, and (alpha) shown by (2) Formula as a result of the numerical analysis by FEM. It is a graph which shows the relationship between the dimensionless intensity | strength (sigma) w / (sigma) o of a joint, and (alpha) shown by (2) Formula as a result of the numerical analysis by FEM. It is a graph which shows the relationship between the dimensionless intensity | strength (sigma) w / (sigma) o of a joint, and (alpha) shown by (2) Formula as a result of the numerical analysis by FEM. It is a graph which shows the relationship between the dimensionless intensity | strength (sigma) w / (sigma) o of a joint, and (alpha) shown by (2) Formula as a result of the numerical analysis by FEM. It is a graph which shows the relationship between dimensionless intensity | strength (sigma) w / (sigma) o of a joint, and (beta) shown by (1) as a result of the numerical analysis by FEM.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1, for example, the welded joint structure of a steel material of this embodiment includes two base metals 1 to be welded to each other and a weld metal (melting material) formed in a groove 2 formed in the base material 1. 3). In the weld joint of this embodiment, the weld metal 3 in the groove 2 is formed in a plurality of layers. That is, in this welded joint, the weld metal 3 is constructed by a welding method composed of a plurality of layers (for example, multilayer welding in which two or more beads are stacked by arc welding).

The weld metal 3 in the groove 2 is composed of a plurality of layers including an initial layer formed first on the route 5 side, and a soft weld portion 6 made of a soft solution that is a weld metal 3 having a strength lower than that of the base material 1. A plurality of beads are further stacked on the soft weld 6 to form a homogeneous weld 7 (homogeneous melt) 7 made of a homogeneous melt that is a weld metal 3 having a strength equal to or higher than that of the base material 1. Has been.
The distance between the two base materials 1 on the route 5 side is a route gap g.

Further, for example, a backing metal 9 is provided on the route 5 side.
In addition, the welded joint structure of the steel material (base material 1) shown in FIG. 1 is an example. For example, in FIG. 1, the groove shape is a mold formed on one base material 1. The V type formed in both base materials 1 may be sufficient.

Here, as shown in FIG. 1, the thickness of the base material 1 is to, the thickness of the soft weld 6 is tw, the root gap is g, the groove width of the groove 2 is W, and the groove The groove angle of 2 is θ.
The base material 1 is premised on a high-strength material of 780 N / mm ² or more (for example, including 1000 N / mm ² class), and the groove shape of the groove 2 of the base material 1 is a re-shaped or It is a V-type welded joint.

The vicinity of the route gap g (the route 5 side) in the groove 2 is welded with a welding material (soft solution) having a strength lower than that of the base material 1 to form the above-described soft weld 6.
By using a low-strength welding material, it is possible to suppress the initial layer cracking and to prevent brittle fracture.

  Welding is performed on the low-strength weld metal 3, that is, the soft weld 6 by the weld metal 3 (homogeneous weld 7) having a strength equal to or higher than that of the base metal. With the above configuration, when an axial tensile force is applied to the base material 1, the high-strength weld metal 3 (homogeneous weld portion 7) is similar to the base material 1 in the low-strength weld metal 3 (soft weld portion 6). ) Gives a binding force when it becomes plastic. The low-strength weld metal 3 (soft weld 6) is constrained by the two base metals 1 and the high-strength weld metal 3 (homogeneous weld 7), giving the soft weld 6 a triaxial tension state. Will be. As a result, it is possible to manufacture a high-strength welded joint. In order to obtain sufficient restraint in the three axis directions, it is necessary that the length of the weld line is sufficiently long. However, in order to obtain a plane strain state in which sufficient restraint is obtained in the weld line direction, The length of the line is preferably 5 times or more the base material plate thickness.

However, if the strength of the soft weld 6 of the weld metal 3 is too small, the strength of the welded joint remains relatively low even if the apparent strength is increased. For this reason, the intensity | strength of the soft molten material as a welding material shall be 490 N / mm < ² > or more. That is, the lower limit strength of the soft weld 6 is defined as 490 N / mm ² . Further, the strength of the soft weld 6 is lower than that of the base material 1. In addition, when low-strength industrial pure iron is used as a welding material having a strength lower than 490 N / mm ² , the low-strength industrial pure iron is low-carbon steel. It is preferable that the strength of the soft molten material is 490 N / mm ² or more from the viewpoint that the manufacturing cost is increased by requiring a charcoal process.

  However, the strength of the welded joint is expressed by the plate thickness to of the base material 1, the thickness tw of the soft welded portion 6 including the first layer on the route 5 side, the groove width W, and the groove angle θ. And the base material strength σo and the strength σs of the low-strength weld metal 3 (soft weld 6) in the vicinity of the route 5. In order to give a sufficiently constrained state to the soft weld 6 and to obtain a welded joint with high joint strength, the parameter β represented by the equation (1) needs to be 0.15 or less.

As it is apparent from the numerical analysis results described above, by setting the 0.15 parameter β which is expressed by equation (1), for example, 780N / mm ² or more, for example, welding 1000 N / mm ² class steels In this case, it is possible to make the strength of the welded joint portion higher than that of the steel material as the base material.

Moreover, the soft weld part 6 including the first layer on the root side of the weld metal has a lower strength than the base material 1, and is approximately equal to or higher than the base material 1 (for example, 780 N / mm ² or more) over the entire weld part. Compared to the case where a high-strength welding material is used, weld cracks are less likely to occur, so prognostic heat management, welding heat input, and interpass temperature conditions are relaxed, and on-site welding productivity can be improved.
Moreover, even if β shown by the equation (1) is 0.15 or less, it is possible to secure the groove width W and the groove angle θ, and the construction is not necessarily performed with a narrow groove. Is possible. This facilitates on-site construction and does not necessarily require special welding skills.

  In addition, in FIG. 1, although this invention is demonstrated using the example of what is called a flat joint which welds the end surfaces of a steel plate, what is called a T-shaped joint which welds the column skin of a building structure, a beam flange, etc., It is obvious that the welded joint structure of the present invention can be applied to all welded joints having a L-shaped or V-shaped groove, such as joints for joining steel pipes.

In the above FEM numerical analysis, the backing metal 9 is ignored and the analysis is performed. However, when the soft weld 6 on the route 5 side is welded, the backing metal 9 is melted and the inside of the weld metal 3 is melted. Therefore, the backing metal 9 is preferably made of a material having a strength equal to or higher than the strength of the soft weld 6.
In addition, as the soft welding material and the homogeneous welding material of this embodiment, known materials corresponding to the base material (steel material) and corresponding to the strength can be used.

1 Base material (steel)
2 Groove 3 Weld metal 5 Route 6 Soft weld 7 Homogeneous weld θ Groove angle W Groove width to base metal plate thickness tw Soft weld thickness

Claims (1)

It is a structure of a steel welded joint that connects steel materials ,
The shape of the groove is a L shape or V shape, and the weld metal in the groove is constructed by a welding method consisting of a plurality of layers,
The strength of the base material to be connected has a strength of 780 N / mm ² or more,
The strength of the soft weld consisting of a plurality of layers including the first layer of the weld metal on the root side connecting the base material is 490 N / mm ² or more and lower than the strength of the base material,
Further, a plurality of beads are stacked on the soft weld to form a homogeneous weld having a strength equal to or higher than that of the base material, and the soft weld is constrained by two base materials and the homogeneous weld. ,
The shape expressed by the thickness to of the base material, the thickness tw of the soft weld, the groove width W of the groove, and the groove angle θ of the groove, the base material strength σo, and the root side A weld joint structure for steel, wherein a parameter β represented by the formula (1) is 0.15 or less from the strength σs of the soft weld.

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